The present invention relates to a display device in which wiring portions of transparent electrodes are metallized, to a display device in which semiconductor chips are mounted based on a chip-on-glass (COG) method, and to a method for inspecting a display panel used in the display device.
A manufacturing method has been devised for the manufacture of a so-called COG type display device in which surfaces of terminal electrodes of a display element are metallized by plating and a semiconductor chip is mounted on the metallized surfaces of the electrodes. This manufacturing method provides a simple means for reducing the resistance value of the terminal electrodes, and therefore achieves, at a low cost, a reduction in the frame area based on the use of fine terminal patterns as well as an improvement in connection reliability.
FIGS. 2A and 2B schematically illustrate a conventional COG type display device. FIG. 2A is a top view of a glass substrate 1 on which the display device is formed, and FIG. 2B is a cross-sectional view of the display device.
Transparent electrodes are formed of an indium tin oxide (ITO) film on the glass substrate 1. The transparent electrodes are patterned in predetermined shapes according to the data to be displayed. Portions of the transparent electrodes are sorted as display electrode portions 4 and wiring electrode portions 6 according to their functions. The glass substrate 1 and an opposing substrate 2 opposed to the glass substrate 1 are attached to each other by a sealing material, with a spacing of about 5 to 7 xcexcm therebetween. A liquid crystal 5 is injected into the spacing and contained in the same in a sealed manner, thus forming a liquid crystal panel.
Pads 7 are formed on terminal end of the wiring electrode portions 6 corresponding to output and input terminal electrodes of a semiconductor chip. The wiring electrodes 6 are laid obliquely with respect to a contour line of the display panel to connect the display electrode portions 4 and pads 7 respectively arranged with different pitches. That is, on a portion of the glass substrate 1 at which the wiring electrodes 6 extend across an end surface of the opposing substrate 2, the wiring electrodes 6 are formed so as to be oblique with respect to the end surface of the opposing substrate 2. Similarly, on a portion of the opposing substrate 2 at which wiring electrodes (not shown) on the opposing substrate 2 extend across an end surface of the glass substrate 1, the wiring electrode on the opposing substrate 2 are formed so as to be oblique with respect to the end surface of the glass substrate 1. As wiring electrodes 6, some electrode groups may be formed depending upon electrode layout artwork. As described above, along an opposing substrate contour line 14 along which a plane defining the end surface of the opposing substrate 2 meets the surface of the glass substrate 1, wiring electrodes 6 exist on some portions of the glass substrate 1 and no wiring electrodes 6 exist on the other portions of the glass substrate 1.
The wiring electrodes formed as described above are selectively plated by nonelectrolytic nickel plating. That is, the wiring electrodes exposed outside the liquid crystal panel (on the glass substrate 1 outside the opposing substrate contour line 14) are selectively plated by nonelectrolytic nickel plating.
As described above, the wiring electrodes 6 are oblique with respect to the opposing substrate contour line at the portion of the glass substrate 1 at which the wiring electrodes 6 extend across the end surface of the opposing substrate 2. The plating liquid has different angles of contact on the ITO surface and the glass substrate surface. That is, the plating liquid has a smaller angle of contact on the ITO surface, and the ITO surface is easy to wet. In contrast, the plating liquid has a lager angle of contact on the glass surface than that on the ITO surface, and the glass surface repels the plating liquid in comparison with the ITO surface. For this reason, the plating liquid can remain easily at a step formed by the glass substrate 1 and the opposing substrate 2 (on the glass substrate portion close to and outside the end surface of the opposing substrate 2) and between an adjacent pair of the wiring electrodes, covering the glass portion where no wiring electrode portion exists. In particular, as shown in FIG. 2A, plating liquid 9 can remain easily between the outermost wiring electrode in the wiring electrode group and another of the wiring electrodes adjacent to the outermost one. A bridge 10 of a nickel thin film can thus form along the periphery of the mass of remaining plating liquid 9 between the wiring electrodes.
After plating, therefore, it is necessary to perform a short circuit check with a probe or to check the existence/absence of such a bridge and to identify a bridging place by image recognition or the like. If one of the formed liquid crystal display elements has a bridge 10, it is necessary to repair a bridged portion by using laser or the like.
In the construction of the conventional liquid crystal display device, as described above, a short circuit can occur easily between wiring electrodes at the time of plating after the assembly of the display panel. Therefore, there is a need to check the existence/absence of such a short circuit. However, a high-priced probe is required for checking because the wiring electrode portions and the pads are arranged with small pitches.
In view of the above-described problems, it is an object of the present invention to provide a liquid crystal display device in which the possibility of a short circuit occurring by means of a plating bridge between wring electrodes is reduced, and in which a short circuit check can be performed by using a low-priced straight probe.
To achieve this object, according to one aspect of the present invention, there is provided a liquid crystal display device having a display element in which, at a portion of an insulating substrate at which a bridge short circuit can occur particularly easily, and at which wiring electrodes on the insulating substrate extend across an end surface of an opposing substrate, the wiring electrodes are formed so as to be perpendicular to the end surface of the opposing substrate.
In another aspect of the present invention, an additional dummy pattern is provided outside the wiring electrodes between which the possibility of occurrence of a bridge short circuit is highest.
In still another aspect of the present invention, probe pads for contact with a probe used for a short circuit check in the liquid crystal display are formed by being arranged in a straight row such that the probe can be simple in structure and can be manufactured at a low cost.